Incandescent body fastener



Aug. 18, 1931. c. BOL 1,819,146

INCANDES CENT BODY FASTENER Filed Junev 28, 1926 4 Sheets-Sheet 1 l6 Mma Aug. 18, 1931.- "-c. BOL 1,819,146

INCANDESCENT BODY FASTENER Filed June 28, 1926 4 Sheets-Sheet 2 /aa-- /es Aug. 18, 1931. c. BOL 1,819,146

IN'CANDESCENT BODY 'FASTENER Filed June 28, 192 4 Sheets-Sheet 3 Aug. 18, 1931. c, 50 1,819,146 I INCANDESCENT BQDY FASTENER Filed June 28, 1926. 4 Sheets-Sheet 4 Patented Aug. 18, 1931 UNETED STATES PATENT OFFICE CORNELIS BOL, F EINDHOVEN, NETHERLANDS, ASSIGNOR TO N. V. PHILIPS GLOEI- LAMPENFABR-IEKEH, OF EINDHOVEN, NETHERLANDS INCAND-ESGENT BODY FASTENER Application filed June 23, 1926, Serial No. 119,083, and in the Netherlands July 2, 1925.

This invention is concerned with the attachment of an incandescent body consisting of one or more stretched filaments in discharge tubes, and electric glow lamps and it has for its object to provide a simple manner of a tachment whereby the filaments are prevented from sagging or curving.

In the use of filaments diificulties have been experienced which were a consequence of the sagging or curving caused by the elongation of the filaments when heated, so that short-circuits between neighbouring wires may occur; the sagging may also be harmful whenthe properties of the tube are de- 1 pendent on the distance between the incandescent cathode and the other electrodes. In order to eliminate these drawbacks it has been suggested to fiX to one or to both ends of the filament a spring whereby the filament is continuously kept taut. In the case of discharge tubes which must permanently be used in a vertical position it has also been proposed to load the incandescent cathode at one of its ends with a small weight.

However, the known devices have the disadvantage that the force required for keeping the filament taut by a pull in a longitudinal direction must be comparatively great while the use of weights entails difficulties during transport.

According to the invention the said difiiculties are obviated by providing such an attaching device for the filaments of .an incandescent body that when the filaments are enlongated they are kept taut by a transverse displacement of one or more of the points of support of each filament. In this case the displacement of the points of support may be so chosen that the mutual distance between neighbouring filaments always remains large enough or that the distance between the filament and the other electrodes is substantially the same;

Although a practical embodiment of the invention can be imagined such that one of the ends of the filament is supported by a wire which is movable in a direction perpendicular to the longitudinal direction of the filament, it is advisable to attach, in accordance with the invention, both ends of each filament to immovable supports and attach one or more of the intermediate points of support are movable to surfaces movable perpendicularly to the direction of the filament. Owing to this construction a rigid at tachment ofthe ends of the filament is possible and a greater effect can be obtained by the transverse displacement of the point of support. v

In an embodiment of the invention one or more sets of supporting wires are provided for the attachment of an incandescent body consisting of at least two parallel filaments, the supporting wires of a set being rigidly connected to each other. Owing to this. construction the different filaments are forced-to curvein the same direction so that shortcircuits between neighbouring filaments are prevented.

In this case the equipotential points of support of the various filaments may be connected to each other by a conducting framework which ismovable in a direction perpendicular to the longitudinal direction of the filaments. The supporting wires connected to one another by a conducting framework form in this manner at the same time an equipotential connection.

The invention oflers special advantages for the attachment of incandescent bodies consisting of anumber of stretched wires located in a circular cylindrical surface. In that case the ends of the filaments are preferably secured to fixed supports. According to the invention, one or more sets of supporting wires for the filaments may be movable around a guide arranged in the axis of the cylinder. At the rotation of the supporting wires about the central guide, the filaments always remain in the same cylinderical surface. I

The invention can also be applied to the attachment of an incandescent body which consists of a U- or Vshaped filament. In that case one or more sets of two supporting wires may be provided, and the supporting wires of a set are secured to an insulating block which is adapted to rotate on a guide arranged in the middle between the'halves of the filament. Also in this case a short-circuit between two filament halves is prevented and the parts of the filament are movable in a cylindrical surface around the central guide or axis. It the incandescent body is composed of a number of parallel connected U- or V-shaped filamentslying on a circular cylindrical surface, there may be provided one or more sets of two frameworks for supporting the filaments and the frameworks of a set may be secured to an insulating block which is rotatable on a guide arranged in the axis of the cylinder.

According to the invention, when heavy currents have to be supplied to one of the ends of the incandescent body, the guide arranged in the axis of the cylinder may consist of a tube inside of which a cooling device is arranged. Besides, the tube may consist of metal parts which are hermetically connected to one another by non-conducting tubular parts. This construction affords the advantags that the frames of supporting wire guides are carried directly by the tube without any insulating intermediate parts.

For the attachment of incandescent cathodes in discharge tubes of very large outputs, for example, more than 100 k. w. in which the incandescent cathode obtains a length such that the current must be led away at more than two points, the guide for rotatable supports may serve at the same time for the supply of current to intermediate points of the incandescent cathode. For this purpose a support which serves to supply current to the cathode may be arranged on the guide so as to be located between the ends of the incandescent body. The cooling device for the guide may consist of a rod or tube which is insulated from the said guide and which serves to carry current to or away from one of the ends of the cathode.

The invention will be more clearly understood by referring to the accompanying drawings which represent, by way of example, some embodiments of the invention. In these drawings:

Figure 1 is a longitudinal section of a discharge tube comprising an incandescent body which consists of a number of filaments located' in a cylindrical surface,

Figure 2 is a section taken on the line II -41 in Figure 1, V

Figure 3 is a section taken on the line IIIIII in Figure 1,.

Figure 4 is a section of a modified construction of the parts represented in Figure 3,

Figure 4a is a longitudinal section of the parts represented in Figure 4,

V Figure 5 is a section taken on the line -V in Figure 1,

Figure 6 is a section of adischarge tube for a large output,

Figure 7 is a section on a larger scale of the discharge tube represented in Figure 6,

Figure '8 is a section taken on the line VIIIVIII in Figure 7,

Figure 9 is a section taken on the line IXIX in Figure 7,

Figure 10 is a section taken on the line XX in Figure 7,

Figure 11 is a section taken on the line X1 X1 in Figure 7,

Figure 12 is a section taken on the line XII-XII in Figure 7,

Figure 13 is a section of a discharge tube in which the guide for the movable supports consists of a number of metal tubular parts which are mutually connected by insulating tubular parts,

Figure 14 is a section taken on the line XIV-XIV in Figure 13,

Figure 15 is a section taken on the line KVXV in Figure 13,

F igure- 16 is an elevation of a stem on which anincandescent body for electric lamps or discharge tubes is mounted, said incandescent body being constituted by a single filament.

Figure 17 is an elevation of a stem on which an incandescent body is mounted which consists of two parallel filaments,

Figure 18 is a cross section of the embodinient shown in Figure 17,

Figure 19 is a detail of an attachment of a U-shaped filament, and

Figure 20 is a. section of a framework which serves to support an incandescent body consisting of a number of parallel U-shaped filaments.

In Figure 1 the reference numeral 1 indicates a metal vessel which serves as anode and which at least partly consists of a material which can easily be sealed to glass, for eXam ple of chrome iron. To the vessel 1 is sealed a glass wall 2 which is provided with an in wardly bent tube which ends in three tubes 3, i and 5. To the tube at is sealed a metal hood 6, for example of chrome iron, on which is mounted a metal support 7 which serves to support grid-shaped electrode 12. For this purpose the support 7 has secured to it by means of a screw bolt a table 8 which is provided with tubular elevations 10 in which supporting rods 9 of highly refractory metal, for example of molybdenum or tungsten, are secured by means of set'screws 11. The supporting rods 9 carry a-grid-shaped electrode 12 which in the construction shown consists of a helically wound wire, for exam-- ple of tungsten. The windings of the helix 12 are kept spaced apart as shown at 13 around the supporting rods 9. In the construction illustrated there are provided two U-shaped rods 9 which at their bent ends are connected to each other by a winding of tungsten wire 14. In the construction the support 7 for the gridshaped electrode is provided with a leading-in wire 34 which is secured to the support by means of a bolt 35.

The tubes 3 and 5 serve to support the incandescent cathode. For this purpose they are shut oit by metal hoods 15 and 16 which tog-ether with the tubes 3 and 5 are cooled by cooling tubes 18 which for example may be made of copper and which are fixed by means of a screw thread in bushes 17, secured to the hoods and 16 respectively. The bushes 17 are provided with apertures 19 which serve for the passage of a cooling agent which is supplied by the tube 18. To the metal hood 15 is secured by welding or in any other manner a rod 20- of refractory material for example, of molybdenum, which at its free end is provided with a number of fiat surfaces 21 against which bear supporting blocks 22 which serve to support the ends of the filaments and which by means of wire windings 23 are maintained in the right position relatively to each other and to the central rod 20.

The metal hood 16 has secured to it a rod 24 which also consists of highly refractory material and which carries a ring 25 of molybdenum or similar material. The incandescent body consists of a number of parallel filaments 26 which are located on. a cylindrical surface. At one end these filaments pass through apertures provided in the ring 25 and at these ends they are provided with loops 27 for the rigid attachment of one end of the filament. At the other end the filaments are secured by means of a wire winding 28 to the supporting blocks 22. Thus both ends of each filament are secured to immovable supports.

For the elimination of any play produced I by the elongation of the filament during its use in consequence of the heating there are provided a number of sets of supporting wires, the wires of a set being united to form a framework 32 (see also Figure 3). The framework 32 is secured to a number of reels 29 of quartz or similar heatproof and insulating material, which are adapted to turn on the central .guide 20. They are maintained in the right position by rings 30 and 31 which are clamped around the guide 20. The framework 32 is provided with a number of eyes 33 through which the filaments 26 pass. The whole framework is adapted to turn on the centrals rod 20 so that at the elongation of the filament the play produce-d thereby can be eliminated by a rotary motion of the framework 32. The latterserves in the construction illustrated at the same time as an equipotential connection between points of the filaments which have been brought to the same potential. It has been found that at the elongation of the filament the frames 32 automatically turn in a determined direction even without being drawn by a spring into a determined direction. This is probably due to the action of the magnetic field existing at the place of the filaments so that these filaments automatically try to move in a determined direction. Often, however, the rotary motion obtained by the filaments themselves isinsufficient to keep the filaments taut. In that casea constructionas that shewn in Figure l and Figure 4a may be useful. In

this constructioncare is also taken for a betwhich bears againsta projection 41 of one of the quartz blocks 37. Between the blocks 37 is arranged a wire frame 42 of highly refractory material such as tungsten or molybdenum, which frame is integral with a fram'e work 43 located in a surface perpendicular to the filament. In the same manner as shown in Figures 1 and 3 this framework is provided with eyes 44 to the number of which corresponds to that of the filaments. In order to prevent the blocks 37 as far as possible from being heated, the wire frame 43 is constructed in such a manner that the heat given off by the filaments to the eyes 44 must go a long way before being transmitted to the blocks 37. The spring 39 is secured, at its one end 45, tothe rod 20 for example by putting this end in an aperture provided in this rod.

' Figures 6 till 12inclusive represent a discharge tube with three electrodes for very large outputs, for example above 200 k. w. In hese figures a metal vessel 51 which serves as anode is sealed to a glass wall portion 52; the metal vessel in the neighbour hood of the weldmust therefore be made of a material which can easily be sealed to glass. The glass wall portion is provided with an inwardly bent tube which terminates in tubes 53. 54: and 55. The end of the mid'dlemost tube 53 is sealed to a metal hood 56 to which a tubular guide 57 is secured by welding or in any other manner. At its end which is turned to the inside, the guide 57 is sealed to a tubular part 58 of insulating material, for example of glass. The tube 57 serves to carry current as will hereinafter be explained and it consists preferably of copper or of similar good conducting material. tubular part which is sealed to the glass part 58 should preferably be made of a material which can readily be sealed to glass. For plainness sake the transition between copper and chrome iron is not indicated in the drawing. A metal hood 59 consisting for example of chrome iron is sealed to the tubular part 58. A hood 60 which is secured to the tube 57 serves to protect the welds at the ends of theglass part 5Sagainst striking electrons. V I

A number of supporting rods 61 consist- However, the

ing of refractory material such as tungsten are secured by means of screws 62 in the hood 59. Inside the tube 57 there is arranged a coolingtube 63 which serves to cool the tube 57 and at the same time to supply current to the end of the incandescent body.- The tube 63 which preferably consists of copper is secured by means of a. screw thread in the hood 59' and at its end it is provided with a number of apertures 64 through which the cooling agent can pass. The mutual distance between the tubes 57 and 63, which must be insulated from each other, is. maintained with the aid of rings 65 of beads (see also Figure 10) said rings being kept in the right position by clamping rings 66 and 67.

The tubes 55 (the discharge tube is provided with two diametrically opposite tubes 55 while the tube 54, which in Figure 7 is indicated as lying in. the surface of drawing, is really turned 90 relatively to that surface) carry hoods 68 to which by welding or in any other manner supports 69 are se cured (see also Figure. 8). The supports 69 carry a table 70 which is preferably made of refractory material for example of molybdenum and which is provided; with bushes 72 in which by means of bolts 74 the ends of a number of supporting rods 73 for a gridshaped. electrode are secured. The rods 73 are preferably made ofmolybdenum or tungsten and carry a helically wound electrode 75 which is kept in the right position by helices 76 which are arranged around the rods 73. At their free ends the rods 73 carry a table 77 to which bushes 78 are secured which receive the ends of the rods 73 and in which screws 79 for the fastening of the rods 73 are provided. The grid-shaped electrode is provided with a leading-in wire 109 which, by means of a bolt, is secured to one of the supporting rods 69 and which leads outside the tube by passing through a pinch 110 provided in a tubular projection of .the glass wall portion 52.

The tube 54 has sealed to its end a hood 80 which can be cooled by a cooling agent which is supplied by a tube 82 which serves at the same time for the supply of current and whichfor this purpose should preferably be made of copper; By means of a screw thread, the tube 82 is secured in a bush 81 which forms part of the hood 80. The wall of the bush 81 presents apertures 83 through which the cooling agent can flow. To the hood 80 is secured by welding or in any other manner a rod 84 of molybdenum or similar refractory material, which carries a ring 85 whichalso consists of refractory material. The incandescent body consists of a number of parallel filaments 86 of which one end 87 forms a loop which is led through an aperture in the ring 85. The other end of each filament is secured to one of the supporting rods 61 by means of a wire winding 88.

. In the tubes for large outputs as those indicated in Figure 6, the great length of the filament necessitates a supply of current to a point lying about midway between the ends of the filaments as, but for a supply of current the current density at one end of the filaments, where not only the heating current but also the emission current must be supplied, would be too great. In the construction shown a number of rods 89 of highly refractory material are secured for this purpose to the tube 57,.for example by welding. The filaments 86 may be secured to these rods by providing in the rods 89 incisions 99 in which the filaments are clamped fast.

The filaments are thus divided in two halves, each half being secured to immovable supporting points. For eliminating the play produced by the elongation of the filaments during their use, there are provided a number of rotatable supports 94 (Figure 7). Around the tube 57 are arranged rings 90 of quartz or similar heat-proof and insulating material, which are held fast by clamping rings 91 and 92. A ring 93 of refractory material is arranged around the ring 90 so as to have some play so that the former ring can easily turn around the quartz ring 90. To the ring 93 are secured a number of supporting rods 94 which are also made of highly refractory material and the ends of which are provided with eyes 95 for the passage of the filaments. The supporting rods 94 are mutually connected by wires 96 which prevent any deformation of the rods 94 and which serve at the same time as an equipotential connection. The quartz ring 90 is provided with a projection 150 around which the end of a helical spring 97 is arranged. The free end 98 of this spring is bent around one of the supporting rods 94 so as to have the shape of a hook and it serves to give the framework 94 a greater displacement than that wnich results from the heating of the filament.

The vessel 51 which serves as anode is provided with a ring 100 by means of which the discharge tube can rest in a cooling vessel. In this case the ring 100 bears on a ring 101 of elastic material (Figure 6) which bears again on aflange 102 of a cooling vessel 103 to which are secured nozzles 104 and 105 which serve for the supply and the discharge of the cooling liquid. For the centering of the discharge tube in the cooling vessel, the anode is provided with a stud 106 which can be tightened by a nut 107. The nut 107 rests against the bottom of the cooling vessel 103 with the interposition of a resilient packing ring 108. I

Figure 13 represents a modified construction of the tube illustrated in Figure 6. In this figure the reference numeral 111 indicates a metal vessel which serves as anode and which is sealed to a glass wall portion 112.

The latter terminates in an inwardly bent tubewhich ends in tubes 113, 114 and 115. To the tube 113 is sealed a metal tubular part 116 which consequently must be made of a material which can easily be sealed to glass such as chrome iron for example. The tubular part 116 is sealed to an insulating tubular part 117, which in its turn is sealed to another metal part 11.6 and so on. The last tubular par 117 of insulating material carries a metal hood 118. The various tubular parts 116 serve to guide a number of wire frames 143 which will hereinafter be described in detail. They are insulated from each other so that afurther insulation between the parts 116 and the wire frame 143 has become useless. Inside of the jointed tube 113, 116, 117

is arranged a cooling tube 119 which serves at the same time to carry current and which is maintained in the right position by projections 120 which are provided there where the outermost tube consists of insulating material. Atits end the tube 119 is provided with a screw thread 121 by means of which it can be securedin the hood 118. Near the end of the tube 119 there are apertures 122 which serve for the passage of the cooling agent. As such may be used compressed air or an insulating liquid.

To the tube 114 is welded at 300 a metal hood 123 which is made of chrome iron or similar material and to which is secured a bush 131 in'which by means of a screw thread a'conductor' 132 is secured. The conductor 132 serves at the same time to cool the hood 123 and the weld 300 and for this purpose it is hollow. In the bush 131 are provided apertures 133 through which the cooling agent can pass to the outside. A rod 124 of molybdenum or any other highly refractory material is secured by welding or in any other manner to the hood 123. The rod 124 carries a ring 125 which is also made of highly refractory material and which serves for the attachment of the incandescent body. The latter consists of a number of parallel filaments 126 preferably of tungsten, which are located on a cylindrical surface and which, at one end, pass through apertures of the ring 125 and end in a loo-p 127. The other end of each filament is secured with the aid of a wire winding 128 to a supporting rod 129 of tungsten or molybdenum which by means of screws 130 is secured in the hood 118.

The tube 115 ends in a metalhood 134 which is sealed to the tube 115 and which carries a rod 135 of molybdenum or similar highly refractory material. If necessary, there maybe provided two tubes 115diametrically opposite each other, each of which carries a rod 135. In that case the tube 114 is turned 90 relatively to the surface of the drawing. The rod or rods 135 carry a table 136 whichis also made of highly refractory material and to which ina manner similar to that indicated in the Figures'l and 7, are secured a number of supporting rods 137 for the attachment of a grid-shaped electrode 139. At theirfree ends the rods 137 carry'a table 138by which the rods are mutually kept in the right position. In order to be able to give the rid the desired potential, there isprovided a leading-in wire 147 which, by meansof a screw 148, is connected to one of the supporting rods 135.

In order to render possible a transverse movement of intermediate points at the elongation of the filaments, which at their ends are secured to fixed supports, a metal ring 140 has been arranged around all'or at least around some of the metal tubular parts 116, said ring fitting the tubular part 116 so as to have some play. The ring 140 com sists preferably of molybdenumand is guided between clamping rings 141 and 142 the latter of which is integral with a helical spring which at its end 145 is bent so as to form a hook. The ring 140 carries supporting rods 143 the number of which corresponds to that of the filaments and which, at their ends, are

provided with eyes 144 for the passage of the filaments. The end 145 of the helical spring bears against one of the supporting rods 143, in consequence of which the framework 140 143 is turned in a determined direction of the filaments admit this. The rods 143 are mutually connected by wires 146, by which the right mutual position of therods 143 is ensured and which act at the same time as an equipotential connection between corresponding points of the various filaments.

Figure 16 represents a stem tube 151 ofan electric lamp or discharge tube, which ends in a pinch 152 which carries two suporting rods 153 and 154. The supporting rods are con nected to leading-in wires 155 and 156 and at their free ends they carry the ends of a filament 157. To the pinch 152 is sealed a glass rod 158 to which is secured a block .159 of chrome-iron or any other material which can easily be sealed to glass. Into the block 159 is screwed a rod 160 to the free end of which a spring 161'is attached, which preferably is made of tungsten and which ends in an eye 162 through which the filament 157 passes. The spring 161 gives rise to a larger transverse displacement of the point of support 162 of the filament than that produced by the heating of the filament. I The Figures 17 and 18 represent a stem tube 165 which ends in pinch 166 which carin .a block 176 of chrome iron or'a similar material which can easily be sealed to glass. This'block is sealed to'a glass rod 177 which together with a glass rod 17 8 is sealed in the pinch. To the rod 175 is secured a leading-in wire 184 which in the usual manner is connected to a leading-in wire 183. The two filaments 171 and 172 are connected in parallel, the current being supplied by the two wires 169 and 170 and carried away by the wire 183.

To the'rod 178 is sealed a block 17 9 for example of chrome iron, in which, by means of a screw thread, a rod 180 is fixed. To the end of the rod 180 is secured a supporting wire 181 which for example may pass through an aperture provided in the supporting rod 180. At its both ends the supporting wire 181 is provided with an aperture 182 through which pass the filaments 171 and 172. By screwing the rod 180 more or less far into the block 179, it is possible to-bend the wire 181 more or less in the shape of an S and thus to cause to act as a spring. At the elongation of the filaments which at their ends are rigidly clamped fast, the points of support 198 will be deplaced by the resilient action of the supporting wire 181 .is a direction perpendicular to the longitudi nal direction of the filament.

Figure 19 represents a detail of an electric lampor discharge tube comprising a filament which has the shape of a U. The metal blocks '185 and 186 which may be mounted in thesame manner for example as indicated in Figure 17 for the block, 176, serve to support the ends of the filament. A rod 187 serves to support the middle of the filament and has secured to its end, with the aid of a wire winding 191, two conducting supporting rods 1 90. To the latter are secured the ends of the two filament halves 188 and 189 which at their other ends are carried by the blocks 1'85 and 186. The rod 18'. is insulatedly mounted'in some manner or other. In order to eliminate any play produced by the elongation of the filament during its use, an insulating block 192 is mounted so as to be rotatable around the rod 187 and by means ofa cross wire 193 it has secured to it two supporting rods 19 1 and 195 which are insulated from each other. If desired, a spring may be secured to the block 192 in the manner shown in Figures 4 and 4a. Owing to the above described device itis possible, even in the case of a U-shaped filament, to render the'movement of the two supporting rods dependent upon each other without their being however in conducting connection with each other.

Figure 20 diagrammatically represents a view of a rotatable support for the filaments in case the incandescent body consists of a number of parallel connected U-shaped filaments. This figu-re shows a block 199 which corresponds to the block 192 in Figure 19 and which is adapted to turn around a central guide 196. To this block are secured a number of supporting rods 200 (three in the I drawing) which are connected to each other byrods 201. The rods 200 may be secured to the block 199 in the manner indicated for the rod 194 in Figure 19. A wire-frame consisting of a number of supporting rods 202 which are mutually connected by supporting rod 203, is arranged so as to be insulated from the wire frame 200-201. The block 199 consequently forms a massive whole with the two wire frames so that at the elongation of the filament all of them are moved in the same direction. The various filament halves which carry current in the same direction are supported by eyes 198 which are secured to the wire frame 200-201 whereas the filament halves which carry curof fixed supports insulated from each other between which a filament 'is attached, an arm engaging the filament at some point between the fixed supports, said arm being free to move transversely of the filament thereby keeping it taut during all variations in length, and a coil spring pressing the arm engaging the filament in a direction transversely of the filament.

3. A filament support comprising a rod, a

pair of supports fixed to said rod between which a. filament is attached, an arm pivoted on said rod and engaging the filament at a point between the fixed supports, and'aspring pressing said arm in a direction transversely to the filament thereby keeping the filament taut.

41. In a discharge tube a filament support comprising a metallic rod, a second metallic rod, a support fixed to each rod and spaced from each other between which a filament is stretched, an arm for the filament extending from one of said rods and engaging the filament at some point between the supports, said arm being free to pivo'ton said rod and insulated therefrom, a spring pressing the arm transversely to the direction of the filament thereby keeping it taut, and electrical leads connected to each rod. I

5. In a discharge tube a filament :suppor't comp-rising :a-metall'ic and, a secondmeta'l lic rod, a support fixed to each rod and spaced from each other between which a filament is stretched, an intermediate filament support mounted on one of the rods and positioned at intermediate points of the filament, said intermediate support being insulated from the rod, an arm extending from one of said rods and engaging the filament at some point between the supports, said arm being free to pivot on said rod and insulated therefrom, a spring pressing the arm transversely to the direction of the filament thereby keeping it taut, and electrical leads connected to each rod.

6. In a discharge tube a support for a filament enclosed in a sealed envelope, comprising a pair of insulated tubes forming a portion of said envelope, a metallic cap sealed in the bottom of each tube, a hollow metallic rod secured to each of said caps and extending to the exterior of the envelope, said metallic rods being of such a size that a space remains between the metallic rod and the insulated tube, openings in the bottom of said hollow rod permitting a cooling agent to circulate through the openings, a metallic rod secured to each of said caps and extending to the interior of the envelope, a support fixed to each rod and spaced from each other between which at least one filament is stretched, an arm for each filament extending from one of said rods and engaging its filament at some point between the supports, said arms being free to pivot on said rod and insulated therefrom, a spring pressing the arm transversely to the direction of the filament thereby keeping it taut, and electrical leads connected to each rod.

7. In a discharge tube a support for a filament enclosed in an envelope, a tube extending within said envelope, a cap sealing the end of said tube, said cap being insulated from said tube by an insulated portion, a

metallic tube secured to the cap and within said first tube of such size that a space remains between the tubes, openings in the bottom of the metallic tube permitting circulation of a cooling agent between the two tubes, a support secured to the cap, a second support spaced from said first support between which a plurality of filaments are stretched, an arm for each filament rotatable about said first tube and engaging its filament at some point between the supports, said arms being insulated from said tube, a spring pressing the arms transversely to the direction of the filament thereby keeping it taut, and electrical leads connected to said metallic tube and said second support.

8. In a discharge tube a support for a filament enclosed in an envelope, a tube extending within said envelope, a cap sealing the end of said tube, said cap being insulated from said tube by an insulated portion, a

- shield protecting said insulated portion from filament spattering, a metallic tube secured to the cap and within said first tube of such a size that a space remains between the tubes, openings in the bottom of the metallic tube permitting circulation of a cooling agent between the two tubes, a support secured to the cap, a second support spaced from said first support between which a plurality of filaments are stretched, an arm for each filament rotatable about said first tube and engaging its filament at some point between the supports, said arms being insulated from said tube, a spring pressing the arms transversely to the direction of the filament thereby keeping it taut, and electrical leads connected to said metallic tube and said second support.

In testimony whereof I afiix my signature, at the city of The Hague, this 10th day 01 June, A. D. 1926.

CORNELIS BOL. 

